1. Field of the Invention
The present invention relates to an article of a mask structure for use in lithography.
2. Description of the Prior Art
A process for manufacturing various products by partial surface modification of workpieces using a lithographic technique is widely utilized in industries, particularly in the field of electronic industry. This process enables a mass-production of products having the same modification pattern on the surface. The surface modification of workpieces can be carried out by irradiation with various sorts of energy, where masks provided locally an irradiation-energy-intercepting material are used to form patterns. The mask hitherto used, when the irradiation energy is visible light, comprises a transparent substrate formed of glass, quartz, or the like which is coated with a pattern of black paint or laminated with a pattern of metal foil or the like opaque to visible light.
In recent years, X-rays and further corpuscular beams such as ion beams have come into use for irradiation with growing needs for the formation of finer patterns and for shorter lithographic processing time. The energy of these beams is absorbed for the most part by the glass or quartz plate which is used in the above-mentioned mask for screening visible light. Consequently, it is undesirable, when using these sorts of irradiation energy, to use a glass or quartz plate for the mask. Thus, the mask used for the lithography wherein X-rays or corpuscular beams are employed for irradiation comprises (1) a film transparent to these beams which comprises an inorganic film such as silicon nitride, boron nitride and silicon oxide films an organic film, such as polyimide, polyamide and polyester films, or a composite film of these materials and (2) an overlying pattern of a metal such as gold, platinum, nickel, palladium, rhodium and indium, opaque to these beams. This type of mask does not have a shape retaining ability by itself and is hence supported by a suitable base. FIG. 1 shows a cross-sectional view of a typical example of this type of mask structure used up to now. This mask structure is constructed by bonding the peripheral portion of a masking-material holding film 2 (hereinafter referred simply to as a holding film) transparent to irradiation energy onto one side (the upper surface in respect to FIG. 1) of an annular base plate 3 with an adhesive 4, the holding film 2 being provided with a desired pattern of masking material 1, which can absorb irradiation energy, on the surface. FIG. 2 is a plan view of the annular base plate 3.
However, the above mask structure according to the prior art has difficulties in securing the flatness of the holding film 2 since the following defects may result depending upon the way of applying the adhesive 4: the thickness of the adhesive layer 4 may be uneven, the adhesive 4 may flow out of the perimeter of the holding film 2, or peripheral parts of the holding film 2 may peel off on trimming the perimeter. These defects tend to cause inaccuracy in lithography.